Interior work and ordinary exterior repairs and maintenance, such as replacing broken window glass or repainting the same colors, do not require the Commission's approval. The exception for interior work is if it affects the exterior, such as the blocking up of a window, in which case the project must be reviewed by the Commission.
The City's Bureau of Code Enforcement can tell you whether a permit is needed for work you are considering. Typically, using ladders and scaffolds in the City right-of-way requires a barricade permit. Replacing (rather than repairing) a window or door requires a building permit.